Events $A$ and $B$ are independent events and $P(A)=P$,$P(B)=\frac{1}{2}$ and $P(A \cup B)=\frac{3}{5}$,then the value of $P$ is . . . . . . .

$A$ bag contains $10$ white and $15$ red balls. If two balls are drawn one after another,what is the probability that the first ball is red and the second ball is white?

Two urns identical in appearance contain respectively $3$ green and $2$ black balls and $2$ green and $5$ black balls. One urn is selected at random and a ball is drawn from it. The probability that it is black is

$A$ purse contains $4$ copper and $3$ silver coins. $A$ second purse contains $6$ copper and $2$ silver coins. If a coin is drawn from any one of these two purses,what is the probability that it is a copper coin?

If $P(A_1 \cup A_2) = 1 - P(A_1^c) P(A_2^c)$,where $c$ stands for complement,then the events $A_1$ and $A_2$ are

$A$ box of oranges is inspected by examining three randomly selected oranges drawn without replacement. If all the three oranges are good,the box is approved for sale; otherwise,it is rejected. Find the probability that a box containing $15$ oranges,out of which $12$ are good and $3$ are bad,will be approved for sale.